Understanding the Paraelectric Double Hysteresis Loop Behavior in Mesomorphic Even-Numbered Nylons at High Temperatures

Novel ferroelectric properties, such as slim double and single hysteresis loop (DHL and SHL) behaviors, are attractive for high energy density and low loss dielectric applications. In this study, temperature-dependent ferroelectric behavior was studied for mesomorphic even-numbered nylons (i.e., nylon-12 and nylon-6) using electric displacement–electric field (D–E) loop measurements. Upon raising the temperature from room temperature to 100 °C, the D–E loops became increasingly narrower, finally leading to slim DHLs with significantly enhanced apparent dielectric constants (i.e., ∼30 and ∼60) and small remanent polarizations (i.e., 3.5 and 8.2 mC/m2) for quenched and stretched nylon-12 and nylon-6, respectively. Combining wide-angle X-ray diffraction and infrared studies, changes in the mesophases and orientation of hydrogen-bonded amide groups after electric poling were used to unravel the structure–ferroelectric property relationship for the even-numbered nylons. At 100 °C, the quenched and stretched ny...